[RC5] Re: Is Rc5-64 taking forever?

Bruce Ford b.ford at qut.edu.au
Mon Mar 9 11:39:31 EST 1998

It has been mentioned that we need to look at growth to get a true 
estimate of time to complete RC5-64.

Using data from the two periods, 5-Dec-97 to 12-Jan-97 and 2-Mar-97
to 6-Mar-97, I did a regression assuming that we should have
exponential growth (and that that growth should have continued
through the DES II period).  That regression gives a time to double
of ~275 days.  

Moore's Law would give time to double of 18 months (365.25*1.5 = 
547.875 days).

I also looked at the possibility of recruiting reducing the time to 
double to 180 days.

Time to double(days)    Keyspace complete    50% keyspace complete
     547.875              Jan 15, 2005          Jul 17, 2003
     275                  May  6, 2002          Aug  4, 2001
     180                  Mar 16, 2001          Sep 17, 2000

To me this shows that within 5 years, 64 bit RC5 encryption will not 
be enough.  If the doubling every 275 days was maintained for 5 
years, d.n could exhaust an RC5-32/12/8 keyspace in 144 days.

Business(and others) need assurance that the standard of encryption 
used will remain viable for much longer that 5 years.

"Time to move to a longer key length".

Bruce Ford                                      b.ford at qut.edu.au
Systems Programmer
Teaching and Learning Support Services          Ph: +61 7 3864 3383
Queensland University of Technology
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